Ion trap mass pectrometer with electrospray ionization

Abstract

A mass spectrometer system with electrospray ion source for generating ions at atmospheric pressure and an ion trap mass analyzer has an improved ion optics for transporting ions from the atmospheric pressure region to the ion trap mass analyzer region. The system comprises a short ion guide having a predetermined characteristic length to radius ratio. The ion guide is coupled to the ion trap mass analyzer via an electrostatic ion optics. The electrostatic ion optics comprises an ion guide extraction optics and an ion trap mass analyzer injection optics. The ion guide extraction optics comprises the ion optical electrode with an aperture that is coupled to an exit of the ion guide and serves as a differential pressure restrictor between the vacuum chamber with the ion guide and the vacuum chamber with the ion trap mass analyzer. The design of the ion optics is tolerant to the mechanical imperfections in the ion optical system and practically eliminates the non-linear matrix effects.

What is claimed is: 
     
       1. An ion trap mass spectrometer system with electrospray ionization comprising: an electrospray ion source for generating ions at atmospheric pressure;   a first, a second and a third vacuum chambers connected in sequence therebetween for passing said ions therethrough, said first vacuum chamber being adjacent to said electrospray ion source;   a sampling device positioned within said first chamber for delivering the ions to said first and second vacuum chambers;   an ion guide positioned within said second chamber for passing the ions from said second vacuum chamber to said third vacuum chamber; and   an electrostatic ion optics and ion trap mass analyzer positioned within said third chamber for passing said ions through said electrostatic ion optics and focusing said ions into said ion trap, said electrostatic optics comprising an ion guide extraction optics and an ion trap mass analyzer injection optics,   said ion guide extraction optics comprising an ion optical electrode having an aperture and coupled to an exit of said ion guide, said optical electrode being a differential pressure restrictor between said second and third chambers.     
     
     
       2. The ion trap mass spectrometer system of claim 1, further comprising a differential pressure restrictor mounted between said first and second vacuum chambers, said restrictor has an orifice. 
     
     
       3. The ion trap mass spectrometer system of claim 2, wherein said ion guide has a length of L and a characteristic radius of r 0 , whereby the length to radius characteristic ratio of L/r 0  equals a value in a range from about 15 to about 50. 
     
     
       4. The ion trap mass spectrometer system of claim 3, wherein said ion guide extraction optics further comprising at least a pair of spaced apart lens electrodes. 
     
     
       5. The ion trap mass spectrometer system of claim 4, wherein said ion guide extraction optics is coaxial to a main axis of said ion guide and is positioned at an exit thereto. 
     
     
       6. The ion trap mass spectrometer system of claim 5, wherein said ion trap mass analyzer injection optics is mounted to a body of said ion trap. 
     
     
       7. The ion trap mass spectrometer system of claim 6, wherein said ion trap mass analyzer injection optics is formed by at least one lens electrode adjacent to an entrance ion trap mass analyzer aperture. 
     
     
       8. The ion trap mass spectrometer system of claim 6, wherein said ion trap mass analyzer injection optics is formed by a pair of lens electrodes that are coaxial to the main axis of said ion trap mass analyzer. 
     
     
       9. The ion trap mass spectrometer system of claim 3, wherein said ion trap mass analyzer injection optics comprises a plurality of lens electrodes that are positioned coaxial to a main axis of said ion trap for receiving extracted ions from said extraction ion optics, refocusing said extracted ions and passing said ion beam towards said ion trap. 
     
     
       10. The ion trap mass spectrometer system of claim 9, wherein a respective independently adjusted potential is applied to each lens electrode of said plurality. 
     
     
       11. The ion trap mass spectrometer system of claim 3, wherein said electrostatic ion optics comprises two pairs of lens electrodes, one pair of said lens electrodes is mounted to an exit of said ion guide and the other pair of said lens electrodes is mounted to an entrance of said ion trap mass analyzer. 
     
     
       12. The ion trap mass spectrometer system of claim 3, wherein said electrostatic ion optics comprises tube lens electrode having a body with a plurality of openings for pumping out neutrals, said tube lens electrode is connected by a first end to an exit of said ion guide and by a second end to an entrance of said ion trap mass analyzer. 
     
     
       13. The ion trap mass spectrometer system of claim 12, wherein said electrostatic ion optics further comprising a lens electrode mounted to said ion trap mass analyzer, and forming with said optical electrode and said tube lens electrode has a three-element electrostatic ion optics, wherein an independently adjustable potential is applied to each said electrode. 
     
     
       14. An ion trap mass spectrometer system comprising: an atmospheric pressure ionization ion source for generating ions;   a plurality of sequentially connected vacuum chambers having a progressively reduced pressure in each chamber of said plurality for passing said ions therethrough;   an ion guide positioned within an ion guide vacuum chamber of said plurality, a longitudinal dimension of said ion guide being comparable with collision focusing length of said ions; and   an electrostatic ion optics positioned within an ion trap mass analyzer vacuum chamber, said ion trap mass analyzer vacuum chamber being adjacent to said ion guide vacuum chamber, said electrostatic ion optics comprising an ion guide extraction optics and an ion trap mass analyzer injection optics,   said ion guide extraction optics comprising an optical electrode having an aperture and coupled to an exit of said ion guide, said optical electrode being a differential pressure restrictor between said ion guide vacuum chamber and ion trap mass analyzer chamber.     
     
     
       15. The ion trap mass spectrometer system of claim 14, wherein said ion guide vacuum chamber is pumped to the pressure in a range from 1-10 -4  Torr.